Photographic silver halide emulsions sensitized with water-insoluble gold compounds



Patented June 16, 1953 i.

I UNITED STATES PATENT OFFICE PHOTOGRAPHIC SILVER HALIDE EMUL- SIONS SENSITIZED WITH WATER-IN- SOLUBLE GOLD COMPOUNDS Rudolph E. Damschroder and Henry C. Yutzy, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester,

' New Jersey N. Y., a corporation vof- No Drawing. Application July 20, 1949,

Serial No. 105,892

22 Claims. (01. 95-7) Thisinvention relates to the sensitization of 2 It is, accordingly, an object of our invention to provide an improved process for sensitizing photographic silver halide emulsions. Other objects will become apparent hereinafter.

In accordance, with our invention, we incorporate in a photographic silver halide emulsion, before or during the final digestion, a water-insoluble gold compound which has-a solubility in soluble silver salt and a Water-soluble halide;

in the presence of a carrier, e. g. gelatin. v (2) Digestion, wherein the above precipitate is heated for a period of time at a"'raised 'te'nr'iperature, e. g. 50 to 60 -C., with or without the addition of further carrier, e. g. gelatin. i (3) Washing, wherein the digested, solidified (e. g. by chilling) emulsion is washed to remove soluble salts.

Melting out and second digestion, wherein the washed emulsion is melted and the resulting flowable emulsion is heated for a period of time, with or without the addition of further carrier, e. g. gelatin.

Of course, variations of the above four, steps can be employed. An emulsion, when used without employing a step, such as (3) ,we call an unwashed, finished emulsion. j An emulsion, when used following completion of all .four steps, we calla washed, finished emulsion. The latter is the type of emulsion generally used.

During the last step, i. e. the melting-out and second digestion, the emulsion increases in sensitivity. To increase the .speed of photographic emulsions various substances have been added at various stages in the preparation of the emulsions. Usually the additions are made during one of the digestion periods. Frequently sulfur compounds, 1. e. so-called sulfur sensitizers have been added, e. g. allyl isothiocyanate, thiourea,

thiocarbanilide, etc., have been added. More re- I cently, it hasvbeen proposed to employ ammonium and/ or metal thiocyanates for this purpose. Still water not greater than the equivalent of 1.0 mg. of gold (metallic) per 100 ml. of water at 25 C. and digest the emulsion in the presence of the gold compound. Gold compounds having a solubility in water as low as, the equivalent of 0.03 mg. per 100 ml. of water at 25 C. can be employed, as can gold compounds of still lower solubility.

- Typical of such water-insoluble gold commore recently water-soluble gold salts have been proposed for the same'purpose. r a .We have now found that the sensitivity-"of photographic silver halide emulsions can: be greatly increased by digesting the emulsions. in the presence of water-insoluble gold compounds rather than water-soluble gold salts, even though the solubility of the gold compounds "is so low that the concentration of gold ions in the emulsionlas compared with the concentrationpbtained when water-soluble .gold salts are. employed) is very low, indeed. I

Any other water-insoluble gold compound which has a solubility in water not greater than the equivalent of 1.0 mg. of gold'per 100 ml. of water at C. can be used in practicing our invention. The water-insoluble gold compounds can be added to the emulsions, before or during the finaldigestion, in solution in suitable organic solvents or as colloidal dispersions. Typical organic solvents include acetic acid, acetone, pyridine, methyl alcohol, etc. Colloidal dispersions in gelatin, polyvinyl alcohol; partially hydrolyzed cellulose acetate, casein can be used.

Advantageously the level of pH during the digestion of. the emulsion, in the presence of the gold compound, is. maintained at or below 9, al-

though this is not essential. Generally speaking the best results are obtained bydigesting the emulsions at a pH of from 5 to 9, in the presence of the water-insoluble gold compound. Digestion of the emulsions in the presence of the gold compounds is. advantageously efiected at from C. to 65 0., although other temperatures can beusedz, A- temperature range of to C. ordinarily gives the best results.

Ordinarily, it is advantageous toemploy a concentration of the water-insoluble gold compound equivalent to from 2.5 to 1000 mg. of gold per kilogram of silver nitrate used in preparing the emulsion; most advantageously a concentration of water-insoluble gold compound equivalent to from 2 to 30 mg. of gold per kilogram of silver nitrate used in preparing the, emulsion is employed.

Advantageously, theemuisions are digested in 4 or a CSSC group- Typical of such sulfur sensitizers' are:

I Calh--S-GHz-CHz-C 0 0H B-Ethyl xanthate propionic acid Normal gelatins contain small amounts of sulfur compounds, such as thiosinamineor allylisothiocyanate, but it is neverthelessfrequentlyadvantageous to add to the gelatin emulsions additional sulfur sensitizers. Beneficial effects are also obtainedby adding: to the emulsions at least one metalv or ammonium thiocyanate, e. g. alkali metal thiocyanates (e. g. sodium or potassium thiocyanate) alkaline earth metal thiocyanates (e. g. calciumv thiocyanate, strontium thiocyanate, etc), cadmium thiocyanate, ammonium thiocyanate, etc. Of" course, thiocyanates containing cations which cations are knownto have, inthemselves, a deleterious effect onsilver' halide emulsions. should. be avoided: Otherwise, the beneficial effects. attained with the. thiocyanate would be partially nullified by the deleterious action. of the cation. Thus. iron thiocyanate which contains .the ironcation should be avoided. One or more sulfur sensitizers or one or more thiocyanates. selected. from the group consisting of metal and ammonium thiocyanates can be employed. Oneor. more sulfur sensitizers can be employed in conjunction with one or more thiocyanates containing a cation selected. from the group consisting of metal and ammonium cations. The sulfunsensitizers and'thiocyanates are advantageously. incorporated in the 3111111! sionsinz the form: of: their solutions in asuitable solvent, such: as water, methyl or ethyl alcohol.

The: sulfur sensitizerscan be incorporated:v in the emulsions atanystageof the preparationof the emulsions, e. g. during; precipitation ofthe silver halides, during the first digestions. (ripening.) enduring: the second digestion of the'emulsi'ons; When incorporating metal and ammo.- nium thiocyanates. in the emulsions prior: to washing,v the-amount. can vary widely. Advan! tageousl'y, however; an amount of thiocyanate equal to. from; about 1 0 to about 75 g. per kilogram of silver nitrate: used in. preparing the emulsion is employedi If the. thi'ocyan'ate: or sulfur sensi tizer is: not. &ddEduntl1i later. in. thepreparation, 6. g.. after washing, it is advantageous:- to. employ;

, in. the. case ot'tlie thiocyanates; anamount-equal the additional presence of at least one sulfur compound, e. g. a sulfur sensitizer, for instance an organic compound containing a C=S group toziromrabout 021:". to about; 10: g, per. kilogram. of silver nitrate used in: preparing. the. emulsionand the. case? of. the. other sulfur; sensitizeraz'an amount equaito' from; aboutimllx to about mg. per": kilogram of! the: silver nitrateaused. in preparing? theiemulsioni.

It: is.- advantageous: to: digest, i'. e. to. heat: treat the. emulsion. with. both the water-insoluble. gold compound and; the sulfurasensitizer. or thiocyanatepresent; at; an appropriate temperature, e. g; atirom lofl to F; During digestion, i.-e:the second digestion as contrasted with thefirst di 5. gesti on or ripeningl the' pH of -tli'eemulsion -is advantageously adjusted to between S -and '7. Maintenance of'the emulsion on the-acid side or'n'eutrality duringcoating'is also advantageous.

I 'The' following examples will serve -to illustrate furtherthe manner of practicing invention.

a batch of gelatino silver-bromoiodidea':emulsion was prepared described by 'I'rivelli and 1 Smith, Phot. J. 79', 330' (1939'), using a precipitation time or about 20 minutes (emulsion No. 11, page 330), except that just before the final digestion of the emulsion, .sodium thiocyanate (1 g. per 1000 g. of silver nitrate used) was added Y to the emulsion; A portion of the emulsion so prepared was coated on cellulose acetat film and dried. The film was exposedina Ib sensitometer at 1 second exposure; using l-watt,-sunlight .quality illumination. The exposed-film waslth n developed in Eastman Kodak, Companys ff-D-l9f developer: for 4 minutes at 2.0 5.0; :Results. are recorded in the-tablebelowlz Further-batches of. gelatino-silverbromoiodide emulsion were prepared. as: described by. Trivelli and Smith; supra; *using azprecipita'tion ztimeeof about "-20 minutesyexcephthat' in eachjcase -j ust before the. final digestion ofathe: emulsiomfa water-insoluble gold compound which. has .aisolu: bility in water notgreater than the equivalent of 1.0 mg. of gold per" 100mllofwater at 25 C. was

added to the emulsion together with sodium. thiocyanate (1 g. per 1000 g. of silver nitrate used). 'A portion of each emulsionso prepared was coated on cellulose acetate film and dried. The dried films were exposed in a Ib sensitometer at /25 second exposure, using 100 watt, sunlight quality illumination. The exp sed films were then .de-

''veloped in Eastman Kodak CompanysfD 10fdeveloper 'for 4 minutes" at 20 C. Result corded in' the follow ing table.

' .ITl l il j 'wstesmsonibn gold =0mpol nd.

. the foregoing i examples :the :marked i n- '-creases.. in photographic.- speed .-that'-l'can-. be ob- -tained in accordance with our inv'ention' are ap pa rent -Water-insoluble goldcompounds whieh-ar ad- .vantageousl-y employed'impracticiri ur nven V .tion can' 'be prepar'ed a's illu'strated in-th follow ing examples.

' was filtered oil and washed on 6. v A solutioncontaining 1g. of auricchloride in 5 cc. of- 95% ethylalcohol jwas added to 50 cc. of

95% ethyl'alcoholcontaining 1.81 g; of-3- fnethyl 2 (3) -thiobenzothiazolone;. (prepared by heating 2 methylmercaptobenzothiazole metho-p-toluenesulfonate in boiling pyridine). The above formulated product separated as a white solid at once. The reaction mixture was stood at about 20 C. 'for several hours and then chilled. The white solid was filtered from the chilled mixture and washed on the filter. with 95% ethyl alcohol.

The yield of colorless crystals-was 98 crude, and 73% after one recrystallization from acetic acid.

I N Y A solution containing 0.34 g. of auric chloride in cc. of 95% ethylalcohol was added to a solution containing 1.11'g. of 3-ethyl-5-E (B-ethyl- 2(3) -benzoxazolylidene) ethylidene] rhodanine in 25 cc. of pyridine and 25 cc. of 95% ethyl alcohol. A reddish solid separated at once. The reaction mixture was stood at about C. for several "hours and then the solid was collected ona filter and washed with 95% ethyl alcohol. The yield of product was 63% crude and 12% after two recrystallization's from nitromethane.'-The-reddish f point 231-232 C. with decrystals had melting composition.

A solution'ficontaining 0.5 g. of auric chloride in 10 cc. of 95% ethyl alcohol wasadded to a hot I suspension of 1.61 g. of 3-ethyl-5-'-(3- ethyl-2(3)- benzothiazolylidene) rhodanine in cc. of acetic acid. The reaction mixture was stood several hours at -about20 C. and .the precipitated solid the filter with 95 ethyl I alcoholi with l=cc.

hot. nitromethane'iif Upon chilling *th'e hot extract, the'crystalswhicli' formed wer i The washedsolid was extracted one recrystallization from nitromethane.

A solution containing "Tgmof auric chloride in cc. of absolute ethyl alcohol was added to a solution containing 0.662. ofg2-methyl-e-naphthothiazole ethochloride in 10 cc. of absolute ethyl alcohol. A pale..yellowsolid separated at once. After chilling for one hour at 0 C., the solid was collected on aeSfilter and washed with absolute ethyl alcohol. Theyield of product was 921% crudeand 53% "after one'treci'ystalllzation fromnitromethane. The' yellow needles gave'"'a very pale yellow. so1ution"in.aeetne.

i H?! H2 e-"enaes ii a x A solution containing :1 gsor-auric 'cfiloride'in 10 cc. of absolute ethylaalcohol was added to a solution containing 0173 g. of2-[2-(l-piperidyl) vinyllbenzothiazole methochloride in 10 cc. of

absolute-ethyl alcohol. After chilling -.for one hour at ,0;.C.- the solid [which separated was collected on a filter and washed with absolute ethyl I 0 alcohol. The yield was 94% crudeand57% after The dark crystals gave a pale yellowso'lution in acetone. .1

A solutioin containing .1 fig. f unt than; in 10- cc. of absolute ethyl-alcohol was: added to a :susperi'sion' of (1.18 g. -01 -5323-diethyl-4.5,4 %5"-di- .benzothiacyanine-Ichloride =inei0 cc.- --of absolute cethyLalcohol. FA darlgsolid wasziormed-atvonce. After chilling for-one .hour at 0? -G. the-solid was collected {011 a iilten and washed witnabsolute ethyl ealcohol. mire-yield was 93% crude and 74% after one recrystallization from nitromethane. The blue crystalsgave-a yellow solution in 'ac etneif 1 V 'd! mum-me ethyl -alcohol -wa;swadded item suspensionot: 0:92 g. 66f 133 diethylthia-e2-cyanine ehlorideilin 'zb cc. ofsabsolute'ethylwalcohol.

. An orange solid separated at once. Afterschilling rmhne hour at .0' C.;'-the solid was'- colledted .25 on aifilter and"washed with absolute ethyl-alco- Zhol. YIh'e JYifild iofz'dye was 89 %"crude' and 71% after Tone recrystallization :from nitromethane. Thereddish conpery needlesjgave an amber-soluti'on in acetone.

1 mm "-"rnin r A lsoluti'oncontainihgleg. of aurio'cliloridein I0 cc. of-absoliite ethyl alcohol was addedto a suspension of 0193 g.oi"'3;3" diethylthiocyanine chloride in 20 cc. of absolute ethyl alcohol. 'A pale orange solid separated at once. After chillingior one hour at fl (l the-solid was collected on a filter and washed with absolute ethyl alcohol. Theyield of dye was" 56% crude.and 38% after one recrystallization from nitromethane. The deep red crystals with a blue reflex gave a -paleyel-lowsolution-in-acetone.

In iai'manner similar to that shownin Ex- 1 59 amplesiz' to 1.1, other similar' organic'water in soluble' gold compounds can beprepared. In

'xtlie benzene nuclei i dfjfithe organic goid corniigpoundsf set forth in -Examples 2 to .11, one or more of the hydrogen atoms can be replaced-by Smuti'Qn containing. i .55 a'zchlorine, a bromine or aniiodine-atom cr b? cyanine chloride in 20 cc. of absolute'ethyl alcohol. A reddish solid separated at once. After chilling for one hour at"0 'C., the solid was collected on a filter and washed with absolute ethyl alcohol. The yield'of dye was 72% crude and 45% after one recrystallization from' nitromethane. The dark green crystals gave a pink solution in acetone. a

1A solutionicontain ing il 5g. oiiauiicQ v :an alkyl or arylgroun le. g. methyL'ethyLpixenyL -:etc. "Ihe preparation-of A1128 .is described-for example byJJ W. *Mllor, A "Comprehensive Treatiseon Inorganic Chemistry, vol. 111, page :by-Gmelin-Krmit; vzapagefifi'lniu) Thegpreparationeof -:AuzSea is described by -:Abegg and-0vebach, Handbuch der Anorg. Chem., vol. H part .1. .page--822, andby GmeIineKraut, page #5 271M) The'gpreparatiomotnul=-is-,described--by .Mellor, .loc. cit -page 608, andiby Gmelin-Kraut,

V2, page 282.

sensitizing dyes of all types can be employed to spectrally (optically) sensitize our new emuligns, 6. g. erythrosin, Congo red, any of the sensitizing cyanine dyes (monomethine, trimethine, pentamethina heptamethine, etc), any of the sensitizing merocyanine dyes (see United States Patent 2,078,233, dated'Ap'ril 27, 1937, for

111W,a?@ 9 thyl-dictumfwasgggqu q example), a y of the-sensitizing hemicyanine emulsions can be made up in the usual manner by coating the flowable emulsions on to a support of a suitable material, such as glass, photo-v graphic paper, cellulose derivative or resin film, etc; to desired thickness, and then setting and drying the coated emulsion.

Our new emulsions can contain hardening agents, setting agents, stabilizing agents, supersensiti'zing combinations of sensitizing dyes or a supersensitizing combination of one or more sensitizing dyes and another substance.

Eastman Kodak Companys D-19 developer has the following composition: I

Water liters 2.0 N-methyl-p-aminophenol sulfate grams 8.8 Sodium sulfite, desiccated 1 do 384.0 I-Iydroquinone do 35.2 Sodium carbonate, desiccated do 192.0 Potassium bromide do 20.0 Water to make liters 4.0

Materials other than gelatin can be employed as the carrier for the silver halide in practicing our invention. Among the non-gelatin silver halide emulsions aresilver halide emulsions prepared using as the vehicle or carrier polyvinyl alcohol (polyvinyl alcoho is herein intended to' include all water-soluble hydrolyzed polyvinyl esters containing an ester group content equivalent to from to- 5% by weight of polyvinyl ester); silver halide emulsions prepared using as the vehicle or carrier hydrolyzed polyvinyl acetate containingan' acetate group content equivalent'to from 59 to 71% by weight of polyvinylacetate; silver halide emulsions prepared using as the vehicle or carrier polyvinyl acetals containing a large proportionof polyvinyl alcohol hydroxylgroups, e. g. polyvinyl acetaldehyde acetals containing polyvinyl acetaldehyde acetal groups equivalent to at least by weight of polyvinyl acetaldehyde acetal and polyvinyl alcohol hydroxyl groups equivalent to at least 15 by weight of polyvinyl alcohol, polyvinyl propionaldehyde acetals containing polyvinyl alcohol hydroxyl groups equivalent to from 45 to by weight of polyvinyl alcohol, and polyvinyl butyraldehyde acetals containing polyvinyl alcohol hydroxyl groups equivalent to from 60 to 80% by weight of polyvinyl alcohol, etc. Any polyvinyl compound, especially those containing only carbon, hydrogen and oxygen atoms, or

those containing carbon, hydrogen, oxygen and amine nitrogen atoms or ammonium nitrogen atoms, which is soluble in a mixture of ethyl alcohol and water (containing from 0 to 50% by volume of ethyl alcohol) to the extent of 10 g. per 100 g. of solvent can be employed as the vehicle or carrier in preparing our non-gelatin silver halide emulsions. Moreover, any other resinous or colloidal material soluble in an ethyl alcoholwater mixture or in water, as stated above, can be employed in preparing our non-gelatin silver halide emulsions, e. g. soluble polyamide resins, such as described in United States Patent 2,384,072, dated September'4, 1945, and hydrolyzed copolymers of vinyl esters and ethylene or propylene, such as described in United States Patent 2,397,866, dated April 2, 1946. Still fur! sions inwhich the silver halide 'is principally 10 ther examples of colloidal materials which can be employed as vehicles or'carriers in preparing our non-gelatin emulsions arehydrolyzed cellulose carboxylic esters, such as hydrolyzed cellulose acetate or hydrolyzed cellulose acetate propionate, containing from 19 to 33% by weight of acyl groups, for example. Any cellulose compound, especially those containing only carbon, hydrogen and oxygen atoms, or those containing only carbon, hydrogen, oxygen andamino nitrogen atoms or ammonium nitrogen atoms, which is soluble in 'a mixture of ethyl alcohol and water (containing from 0 to 50% alcohol) to the extent of 10 g. per g. of solvent can be employed as the .vehicle or carrier in preparing our sions.

In connection with the non-gelatin colloidal materials, such as polyvinyl'alcohol the silver halide emulsions can be prepared using gelling agents, such as phenols, e. g. orcinol, gallic acid, 2,4-dihydroxybenzoic acid, 4-chlororesorcinol, o: naphthol, phloroglucinol, 2,7-dihydroxynaphtha-- lene, etc. Moreover, the non-gelatin silver halide emulsions can be prepared using silver halide dispersingagents, e; g'; starch acetate, gum arabic, a copolymerof maleicanhydride and vinyl acetate,'low viscosity methyl cellulose, water-soluble amino carbohydrate dispersing agents (e. g. diethanolamine cellulose acetate or any other of these agents described in' United States Patent 2,360,238, dated October 10, 1944) amino resin dispersing agents (e. g. dimethylaminobenzaldehyde acetals ofpolyvin'yl alcohol, or water-solunon-gelatin silver halide emulble polyvinyl acetals in which at least a part of the acetal groups are 4'formylphenyltrialkylammonium saltacetal'grouDs, such as the polyvinyl acetal of 4formylp'henyl 'trimethylammonium methylsulfate and other such compounds described in United States Patent 2,358,836, dated September 26, 1944), etc.

Polyvinyl compound silver halide "emulsions and their preparation are described in United States Patents 2,286,216, dated Junelfi, 1942; 2,276,322, dated March 17, 1942; 2,276,323, dated March 17, 1942; 2,311,058, dated February 16, 1943;

2,311,059, dated February'lfi, 1943; 2,367,511,'

gelatin proteinswhichihave been converted to a derivative thereof, e. g.' 'by reactionw'ith-a sulfonyl chloride; a carboxylic chloride, 'a carboxylic' anhydrid'e, an i'so'cyanate, a 1,4-diketo'neor acrylonitrile, and then oxidized, e.'g. with hydro-.

gen peroxide, as described in the copending application of Wesley G. Lowe and John W. Gates, Jr. Serial No. 768,480, filed August 13, 1947, can also be employed.

Our invention is directed especially to the sensitization .of photographic silver halide emulsilver bromide, but canbe employed with any silver halide emulsion, particularly the customary silver chloride, silver chlorobromide, silver chlorobromoiodide;silver chloroiodide, silverbromide and silver, bromoiodide developing-out emulsions.

halide emulsion in which thesilver halide is prinby volume of ethyl Proteins, such as casein,

By the term photographic silverassess-1:.

cipally: silver: bromide, wermean a photographic silverihalideemulsiorr in; which from 60to' 100%- of: the weight" of the silver halide is silver'i bromide.-

What we claimos: ouninventiorr and desire toibe secured by Lettersi-Patent 'of." the- United States is:

l". A. process" for." sensitizing a photographic: silver halide emulsion comprising adding to the emulsion, before" or duringi'finali digestion a water insoluble gol'd compound" which has a:

solubility in;.water::equivalent to from :03 mg: to:

silver halide developing-out emulsion comprising:

addingto the emulsion; before or duringfinal dige'stion',- a. water-insoluble goldcompound whichhas a'solubility in water equivalent to from 0.03:mg.:to"1;0 mg. of gold per I00 ml. of water" at 0., and digesting the emulsi'onin the presence of the water-insoluble: gold'compoundi 3. A pr'ocess' -for" sensitizing a photographic gelatino-silver-halide developing=ouu emulsion comprising: adding to J theemulsion; before or during" final digestion; a; water-insoluble-gold compound which has a solubility'in water 'e'quivalent to from 0.03 mg? to llo mgi OfgOld per 100 ml. or water at 25 Grand: digesting :the emulsion.

in the presence of" the water insoluble goldcompound.

4. A. process for sensitizing a. photographic gelatino-silver halide developing-out emulsion in: which the silver" halide is.- principally siliver' bromide; comprising adding? to the emulsion, before or during finaldigestiong. az'water insoluble gold compound which has a solubility in water'- equivalenttd from 0.03-mg: to: 111mgof gold per 100 ml. ofwater at 25 0., andLdigeSting-theemulsion in.- the presence of the watereinsoluble gold: compound;

53 A process for sensitizing a photographic gelatino-silver-halide developing-out emulsion in which the silver halide is: principally silver bromide comprising adding to. the: emulsion; before or during fi'nal digestion, a. sulfur sensiT-- tizer and a water-insoluble gold compound'fwhich has asolubility inwater equivalent. to from 0.03 mg; to 1.0 mg; of gold: per 100 ml. of water at 25 C., and digesting the emulsion in thepresence of" the gold compound: and: the' sulfur sensitizer;

6; A process for? sensitizing a'zphotographic' gelatino-sil'ver-halide developing out emulsion in which the silver halide is": principally silver.

bromide comprising adding to the 'emulsion; be fore or during'final. digestion, a sulfur'sensitizerand a water-insoluble.goldv compoundzwhich has a solubility in water equivalent to fromxOlOhmg:

85A processfforzsensitizing a; photographick gelatinm-silver-halide developing-out. emulsion-in; whichzxthe silver. halide: is'.-=principal1y "silver? bromide comprising adding, to r the. emulsion, bee fore or during; finah. digestion; sodium; thio.:- cyanate and a water-insoluble gold-;rcompound;; which has a solubility in:waterequivalenttmfrbm 0.03tmg; to 1.0 mg. of goldper 100 ml. ofwaterr at 25 C.:anddigestingzthe emulsion. in the-pres. ence: of the gold. compound and the thiocyanate r. onrthe" acid sid910f: neutrality.

9.: A: process for sensitizing.. a photographic gelatino-silver-halide developing-out emulsion-:ini. which: the silverhalide is. principally; silver bromide comprising-padding to: the emulsiombe! fore enduring final-digestion;sodium-thiocyanaterin a. concentration of from 0.1 to 10% gramsmer: kilogram of silver: nitrateemployed in preparing. the emulsion and a; water-insoluble gold. .compound which has a solubilityr in water-eduivaientw to from 0.03 mg. to 1.0 mg. of gold per 100 ml.. of 'water"at*25 C., in' agconcentrationof from' 215' to. 30 mg." per kilcgramof silver nitrate emplayed in preparing theemulsi'on, and digesting: the emulsion in'the presence of the thiocyanate" and the gold' compound on the" acid sideot neutrality.

10. A process for sensitizing a; photographic gelatino silver-bromoiodide developing-out emulssion comprising adding to the emulsion; before? or during final digestion sodium th-iocyanatein arconcentration of from- 0.1- .tol0r'grams per'kilorgram of silver nitrateemployedinpreparingqther emulsion and aurous sulfide (Auas) inv 250011?" centration oi -from 2.5 to!30 mg. per .kilogram ot silver nitrate: employed in. preparing theemul sion, and digesting the emulsion in the presence: of the thiocyanateand?the aurous--'sulfide onthe acid side of neutrality.

11. A process;

for sensitizing; a photo graphic gelatino-silver-bromoiodide developinggout. temulsion' comprising-adding, to the?emu1si0n,.;

in a concentration of from 2.5 to 30 mg. perk'il'ogram of emulsion employed in preparing" the emulsion; and digesting the emulsion in the presence of" the 'thiocyanateand the gold compound' on theacid side of neutrality;

to 1.0 mg. of gold per'lllo' ml: of water at'25'f C.,'

and digesting 1 the emulsionin the presence ofthe gold compound" and the'sulfur sensiti'zer; on the acid side of neutrality.

'7. A process for sensitizing" a: photographic gelatino-silver-halide d'eveloping-outemulsion in which the silver halide is principally silver bromide comprising'addingto'the emulsion, before or during'final digestion, an alkali metal thiocyanate and a water-insoluble gold" compound which has a solubility'in waterequivalent to from 0.03 mg. to 1.0m. of gold per 100 ml. of water at 25 C.', and digesting the emulsion in the presence of the gold'compound'and the thincyanate; on the acid 'sideofneutrality;

12. A process for sensitizing aphotographic gelatino-silver-bromoiodide developingout emulsioncomprising adding to the emulsion, before or during final digestion, sodium thiccyanate in a concentration of from 0:1 to' 10 grams per'kilogram' of silver nitrate employed in preparing the emulsion and thegold compound represented by the following formula:

. 13 in a concentration of from 2.5 to 30 mg. per kilogram of silver nitrate employed in preparing the emulsion, and digesting the emulsion in the presence of the thiocyanate and the gold compound on the acid side of neutrality.

13. A process for sensitizing a photographic gelatino-silver-bromoiodide developingout emulsion comprising adding to the emulsion;-

before or during final digestion, sodium thiocyanate in a concentration of from 0.1 to

grams per kilogram of silver nitrate employed in preparing the emulsion and the gold compound represented by the following formula:

AIlCh cording to the process of claim 13.

' Numb 81' 14 in a concentration of from 2.5 to 30 mg. per kilogram of silver nitrate employed in preparing the emulsion, and digesting the emulsion in the presence of the thiocyanate and the gold compound on the acid side of neutrality.

15. A process for sensitizing a photographic silver halide emulsion comp-rising digesting the emulsion in the presence of a waterinsoluble gold compound which has a solubility in water equivalent to from 0.03 mg. to 1.0 mg. of gold per ml. of water at 25 C.

1-6. The photographic emulsion obtained COIdiIlg to the process of claim 1.

17. The photographic emulsion obtained cordingto the process of claim 15.

18. The photographic emulsion obtained cording to the process of claim 10. p

19. The photographic emulsion obtained cording to the process of claim 11.

20. The photographic emulsion obtained cording to the process of claim 12.

21. The photographic emulsion obtained 22. The photographic emulsion obtained according to the process of claim 14.

RUDOLPH DAMSCHRODER. HENRY C. YUTZY.

References Cited in the file of this patent UNITED STATES PATENTS Name Date 2,399,083 Waller et a1. Apr. 23, 1946 FOREIGN PATENTS Number Country Date 608,667 Great Britain Sept. 20, 1948 OTHER REFERENCES Bureau of Standards Journal of Research, vol. 1, October 1928, pages 565-588; pages 575-588 particularly cited. 

1. A PROCESS FOR SENSITIZING A PHOTOGRAPHIC SILVER HALIDE EMULSION COMPRISING ADDING TO THE EMULSION, BEFORE OR DURING FINAL DIGESTION, A WATER-INSOLUBLE GOLD COMPOUND WHICH HAS A SOLUBILITY IN WATER EQUIVALENT TO FROM 0.03 MG. TO 1.0 MG. OF GOLD PER 100 ML. OF WATER AT 25* C., AND DIGESTING THE EMULSION IN THE PRESENCE OF THE WATER-INSOLUBLE GOLD COMPOUND. 